The present invention relates to a particle separator for removing particles from an exhaust gas stream of an internal combustion engine. The present invention also relates to a method for removing particles from an exhaust gas stream of an internal combustion engine.
During combustion in a diesel engine, and also during direct injection with a spark ignition engine, emissions of particles occur that among other reasons result due to the incomplete combustion of the fuel, and predominantly comprise carbon black. To burn this carbon black, GB 895,990 A proposes burning or treating them with NO2 as oxidizing agent instead of oxygen.
It is furthermore known from U.S. Pat. No. 4,902,487 to separate off carbon particles at a filter, and to subsequently oxidize the particles with NO2. To produce the NO2 pursuant to DE 28 320 02, for example, the NO contained in the exhaust gas stream of the internal combustion engine can be oxidized on a platinum-containing catalyst to form NO2. The proportion of NO2 in relationship to the total NOx is thereby significantly increased, whereby this reaction occurs starting at approximately 180° C. In contrast, the combustion of the particles by NO2 begins at temperatures starting at 250° C. A particle oxidation in the gas phase practically does not occur. For this purpose, a deposition on a solid material is necessary in order to ensure an adequate retention time, which is generally realized by the use of a particle filter.
A significant drawback of such a procedure, however, is the high exhaust gas counter pressure that is caused by the filter. This becomes noticeable by an increased fuel consumption. In addition, during the operation non-combustible constituents are also deposited on the filter, such as lubricating oil ash. As a result, the exhaust gas counter pressure continuously increases, so that the filter must be regularly and frequently replaced in order to avoid an even greater fuel consumption, and possibly also damage to the internal combustion engine. Furthermore, insufficient oxidation can result in an ever increasing coating with soot, which can ultimately lead to clogging of the filter.
To avoid these drawbacks, it is already know from EP 1 072 765 B1 to use a particle separator that has no filter, whereby the exhaust gas stream is guided along a structural surface and is constantly deflected, in order to be able to remove or separate very fine particles out of the exhaust gas stream, in particular by diffusion. However, the drawback of this is that due to the constantly changing exhaust gas temperatures and the constantly changing NOx raw emissions of intermittently operated internal combustion engines, as is the case with motor vehicles, there is often insufficient NO2 available for oxidizing the removed soot. This means that the particle separator must store the particles for a sufficient length of time until at a later point in time sufficient NO2 is present for the oxidation of the removed soot. To ensure this, it is proposed in DE 101 53 284, in DE 101 53 283, and in DE 201 178 73 U1 to store the removed particles in a fleece or fiber layer. However, the quantity of particles that can be stored in this manner is relatively small due to the small volume of the fleece. Furthermore, the manufacture of the fleece is very expensive.
In contrast, it is an object of the present invention to provide a particle separator, as well as a method, for removing particles from an exhaust gas stream of an internal combustion engine, by means of which particles can be reliably removed from the exhaust gas stream in a straightforward manner.